Modern aircraft commonly contain IFEC systems for providing media to passengers. The audio component of this media is supplied to passenger headphones via a Remote Jack Unit (RJU) typically installed in the armrest of an aircraft seat.
An RJU typically supports one or more of the following headphone configurations commonly used on aircraft: 1) conventional analogue headphones; 2) powered noise-cancelling headphones; and 3) non-powered active noise-cancelling headphones. Each of these headphone configurations is typically connected via one or more 3.5 mm and/or 2.5 mm diameter plugs with a layout defined by an ARINC (Aeronautical Radio Incorporated) standard.
With the introduction of digital audio to IFEC systems, it has been proposed to add support for connecting digital headsets to an RJU. One proposed solution is a jack that supports digital audio, but can also detect the presence of a conventional analogue headphone and output an analogue audio signal instead.